Switching arrangement for coupling a transmitting unit to a transmission line

ABSTRACT

A switching arrangement is provided for coupling a transmitting unit to a transmission line. According to the present invention, a transformer is provided, whose secondary winding is a portion of the transmission line and whose primary winding is connected with the transmitting unit and integrated into a parallel resonance circuit, whose resonant frequency is tuned, each time, to the carrier frequency of the transmitted signal. In addition, a tuning unit may be provided for the automatic tuning of the parallel resonance circuit.

FIELD OF THE INVENTION

The present invention pertains to a switching arrangement for coupling atransmitting unit to a transmission line.

BACKGROUND INFORMATION

For the supply or the removal of signals, connecting leads are oftenconductively connected with two wire conductors. During couplings ofthis type, in order to make contact it is necessary each time to removeor pierce the insulation layer of the two wire conductor. A multiplecoupling of connecting leads results in damage to the two wireconductor. In addition, the unallowed coupling of unauthorized thirdparties onto the two wire conductor is easily feasible. In a telephonenetwork utilizing conductive coupling, unauthorized parties can readilyswitch on. European Patent Publication No. EP-OS 0 417 542 discloses anapparatus for the inductive coupling of sending coils to a two conductorwire which largely eliminates such problems. Therein, a three-limbedferrite core is utilized, whose yoke, for the insertion of the couplingcoil or the two wire conductor is so pivotally arranged, that the twowires of the transmitting line accordingly pass through the center limband one of the two outer limbs. For example, the coupling coil connectedwith the transmitting unit surrounds the center limb with severalwindings. For the transmission of information between two subscriber endunits coupled to the transmission line, the transmitter generates amodulated high frequency signal to the primary coupling coil, whichsignal transforms the transformer, comprised of the coupling coil andthe transmission line, and carries same, via the secondary-sidedtransmission line to the receiving end unit. The primary-sided perceivedload Z1 of the transmitter ideally corresponds to the product of thesecondary-sided contacting load Z2 and the square of the transmissionratio (N1/N2). Parallel thereto, the relatively small main inductivityof the transformer makes an appearance, which requires an amount ofcurrent which exceeds, many times, that of the transformed load orresistance Z1. The main capacity becomes particularly small if thesecondary windings, formed via the transmission line, has only a fewwindings. The inductive coupling is thus problematic only fornonsystem-connected terminal units, which, for example, only have verylow supply voltages available and which can supply only small outputs.Normally, with such terminal units only a limited range can be achieved,within which there is a satisfactory signal to noise ratio. If, forexample, in order to increase the range, the output to the transmissionline is increased, there is a reduction of the life span of thebatteries that feed the terminal unit. In terminal units, powered by thenetwork, a correspondingly larger dimensioned current supply unit wouldhave to be provided.

SUMMARY OF THE INVENTION

The basis for the task of the present invention is to provide aswitching arrangement which avoids the described disadvantages.Particularly, the range between the individual terminal units should beincreased, the output removal of the terminal units should be reducedand the signal to noise ratio should be enhanced.

This task is achieved via the measures set forth in the specificationand the characterizing portions of the claims. Advantageous embodimentsof the invention are also set forth in the specification and the claims.

By the use of the method of this invention and the switchingarrangements of the present invention, the amount of current that mustbe fed to the coupling unit is greatly reduced, which is particularlyfavorable for non-system-connected operated terminal units. With thesimultaneously reduced current supply, the output of the transmissionline is increased. The quality of the transmitted signals is thusgreatly enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter in more detail, by way ofexample, with reference to the drawings in which:

FIG. 1 illustrates a switching arrangement of the present invention witha transformer whose primary winding is interconnected with atransmitting unit;

FIG. 2 illustrates a switching arrangement of the present invention withtwo primary-sided auxiliary windings; and

FIG. 3 illustrates a transmitting unit with a device for the automatictuning of a resonating unit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a transmitting unit TR, which is coupled to a couplingunit, that is the primary windings of a transformer TF1, to transmissionLine UL, which forms the secondary winding of transformer TF1. Thissecondary winding normally includes only one winding. Transmission unitTR, which gives off a modulated high frequency signal, comprises, forexample, a preamplifier and a final amplifier. The main inductivityresulting from the described details requires very high current, whichvia the generally utilized supply sources, particularly supply sourcespowered by batteries, cannot be extracted or not extracted for anextended period of time. This problem is solved via the hereinafterdescribed utilization, as per this invention, of a passive currentamplifier. The switching in of one or more capacitors C1, . . . , Cn,via switch S1, . . . , Sn, onto winding W1 forms a parallel resonancecircuit, which can be tuned to a high and/or carrier frequency. Thetuned resonance circuit acts in this manner as a pure resistance Rp. Thecurrent, which conforms to the quotient of voltage Ur and the effectiveresistance Rp achieves the minimum value at resonance. In the reactiveimpedance, at that time, resonance streams Ir are pulsating whichachieve much higher values than the current I flowing in from theoutside. Thus, with lesser power supplied from the outside, greatercurrents can be induced in the secondary windings. Of course, tuneablecapacitors (variable capacitors Cd, capacitance diodes Cv, etc.) canalso be advantageously utilized.

In FIG. 2, transmitting unit TR is connected with a first spool,respectively, winding W1 of a transformer TF2. Via the use of spools,respectively windings W2, W3 of transformer TF2 and capacitors C1, . . ., Cn, a tuneable parallel resonance circuit is formed on the primaryside which is coupled in a transformer-type manner to winding W1.Capacitors C1, . . . , Cn can be switched on upon demand. Winding W3 isprovided for switching same, via switch Sw, onto winding W2 so that theresistance circuit is tuneable over a wider region. In this manner itcan also be provided that winding W2 or winding W3 can singly, or thatwindings W2, W3, serially switched together, can be switched ontocapacitors C1, . . . , Cn.

FIG. 3 shows a switching arrangement according to the present inventionin which the parallel resonance circuit is automatically tuneable. Theprincipal item of the switching unit is tuning unit T via which thecapacitors C1, . . . , Cn and the windings W3 and/or W2 are thuslyalways switched on so that the resonance frequency of the resistancecircuit continuously changes, until the switching unit takes notice thatthe carrier frequency is close enough to the carrier frequency of thesending signal. It has been found to be advantageous to maintain thecurrent I, outgoing from transmitting unit TR to winding W1, and tomodulate the resonance circuit, until current I is minimal or below apredetermined threshold value. The minimal value of current I, as perthe previous explanation, always occurs when, at the sending unit, onlythe relatively high resistance Rp of the measurement circuit occurs. Theminimal value of current I thus only occurs in the case of resonance.The illustrated switching arrangement is comprised of a bistable or flipflop toggle stage BST-KS whose outlet is connected with the inputs of aclock generator C and a counter Z, which are contained in tuning unit T.Transmitting unit TR is connected, via a resistance Ran, with winding W1and the input of a rectifier stage RECT, whose output and a line REF,which includes a voltage threshold, are each connected with the input ofa comparator COMP. The output of comparator COMP, as well as a signaland command line S&IO, connected to a non-illustrated control unit, eachare also connected with the input of flip flop toggle stage BST-KS. Theoutput of flip flop toggle stage BST-KS is additionally connected, via amonostable toggle stage MST-KS, with a control unit, respectively vialine S&IO, via which the signals of the transmitting unit TR that are tobe transmitted, are channelled thereto.

The switching arrangement of FIG. 3 functions as follows: A start signalfor the tuning procedure is channelled to the flip flop toggle stageBST-KS via line S&IO, whereinafter clock generator C and counter Z,connected with toggle stage BST-KS, are activated. Counter Z, whichreceives timing signals from clock generator C, begins the countingprocedure from an existing or freely chosen count of the counter.Counter Z can be a simple dual counter whose outlets switch, viaswitcher So, . . . , Sn, respectively Sw, capacitors C1, . . . , Cn orwindings W3 and/or winding W2, onto the resonance circuit. Switches SO,. . . , Sn, respectively Sw, are, for example, activated via switchingtransistors. The capacitors C1, . . . , Cn and windings W are chosencorresponding to the value of the counter outputs, so that a uniformtuning procedure is achieved. Transmitting unit TR outputs, during thetuning procedure, a signal, having the desired carrier frequency, towinding W1. Via resistance Rm a voltage, proportional to current I, istapped and channelled to the input of rectifier Stage RECT, which inturn channels a corresponding DC voltage to the input of comparatorstage COMP. In case this voltage, close to resonance, is smaller thanthe voltage threshold delivered to comparator stage COMP, via line REF,a signal is sent to flip flop toggle stage BST-KS, whereafter the sameis set back. Via the setback of flip flop toggle stage BST-KS, clockgenerator C and counter Z are stopped, so that the current count of thecounter is retained. In addition, monostable toggle stage MST-KS isactivated, which reports back the successful conclusion of the tuningprocedure to the control unit, via lead S&IO. In order to reduce thenumber of connecting leads, the sending signal and the command signalare carried on only a single line. The signals are channelled to togglestage BST-KS preferably via a Schmitt trigger, which transforms theincoming signal into a clean square wave signal. In the interest ofsimplicity, of course separate command leads can be used, which areseparated from the sending signal leads. Preferably, counter Z isconnectable with a D/A converter, which outputs a voltage, proportionalto the count of the counter, to a variable capacitor Cd, Cv.

In addition, for uses in the telephone field, normally a tuningarrangement is utilized not only for the voice channel but also for thesignal channel. Generally, only a single frequency is assigned to thesignal channel. In contrast thereto, the voice channel utilizes severalcarrier frequencies, which can be dispersed over a wide frequencyregion. This means that the resonance circuit of the voice channel mustbe tuneable over a wider region, which can be achieved through thepotential switching on of windings W3 and/or W2. The signal channel andthe voice channel therein include a switching arrangement which, inprinciple, corresponds to the arrangement shown in FIG. 3. Clockgenerator C can be jointly utilized for both channels, or switched onvia an OR-gate. Also, the acknowledgement pertaining to the terminationof the tuning procedure of the signal or voice channels can beaccomplished via a joint line.

In addition, the tuning arrangement could be constructed with the aid ofa microprocessor. Therewith however, a greater capacity would berequired.

In case the transmitter is switched off upon the termination of aconversation, the count of the counter is retained. In addition, when,in place of transmitting unit TR, a substitute resistance is switchedonto winding W1, the impedance ratios in transmission line UL remainconstant.

I claim:
 1. A switching arrangement for coupling a transmitting unit,that generates a signal to be transmitted, to a transmission line,comprising a transformer having a primary winding that is connected withthe transmitting unit and a secondary winding that is part of thetransmission line, and a parallel resonance circuit which is tuneable toa carrier frequency of the signal to be transmitted, the primary windingof the transformer being part of the parallel resonance circuit.
 2. Theswitching arrangement of claim 1, wherein the parallel resonance circuitis tuneable in such a way that a voltage applied to the parallelresonance circuit achieves a predetermined maximum value or exceeds apredetermined threshold value.
 3. The switching arrangement of claim 1,wherein the parallel resonance circuit comprises a plurality ofcapacitors that are selectively connected in parallel with the primarywinding of the transformer.
 4. The switching arrangement of claim 3,further comprising a tuning unit for tuning the parallel resonancecircuit, a resistive element that is connected between the transmittingunit and the primary winding of the transformer for providing a voltagethat is proportional to the current supplied to the parallel resonancecircuit, a rectifier which rectifies the voltage applied to the parallelresonance circuit, and a comparator that is provided between therectifier and the tuning unit for comparing an output voltage of therectifier with a voltage threshold value and for stopping a tuningprocedure by the tuning unit after exceeding the voltage thresholdvalue.
 5. The switching arrangement of claim 3, wherein the parallelresonance circuit further comprises a plurality of switches forselectively connecting the capacitors in parallel with the primarywinding of the transformer.
 6. The switching arrangement of claim 3,wherein the primary winding comprises one or more windings that may beselectively connected in series.
 7. The switching arrangement of claim1, wherein the parallel resonance circuit is tuneable in such a way thatthe current supplied to the parallel resonance circuit achieves apredetermined minimum value or is less than a predetermined thresholdvalue.
 8. The switching arrangement of claim 1, wherein the parallelresonance circuit comprises tuneable capacitors that are connected inparallel with the primary winding of the transformer.
 9. A switchingarrangement for coupling a transmitting unit, that generates a signal tobe transmitted, to a transmission line, comprising:a transformer havinga primary winding that is connected with the transmitting unit and asecondary winding that is part of the transmission line; a parallelresonance circuit which is tuneable to a carrier frequency of the signalto be transmitted, the primary winding of the transformer being part ofthe parallel resonance circuit; the parallel resonance circuitcomprising a plurality of capacitors that are selectively connected inparallel with the primary winding of the transformer; a tuning unit fortuning the parallel resonance circuit; a resistive element that isconnected between the transmitting unit and the primary winding of thetransformer for providing a voltage that is proportional to the currentsupplied to the parallel resonance circuit; a rectifier which rectifiesthe voltage applied to the parallel resonance circuit; a comparator thatis provided between the rectifier and the tuning unit for comparing anoutput voltage of the rectifier with a voltage threshold value and forstopping a tuning procedure by the tuning unit after exceeding thevoltage threshold value; and a command line which is connected via aSchmitt-trigger with a first input of a flip flop toggle stage having asecond input that is connected with an input of a monostable togglestage, the monostable toggle stage also including an output that isconnected with the command line; the resistive element being connectedon one side with an output of the transmitting unit and on the otherside with the primary winding and also being connected, via therectifier, with a first input of the comparator having a second inputthat is connected with a reference line providing the voltage thresholdvalue.
 10. A switching arrangement for coupling a transmitting unit,that generates a signal to be transmitted, to a transmission line,comprising:a transformer having a primary winding that is connected withthe transmitting unit and a secondary winding that is part of thetransmission line; a parallel resonance circuit which is tuneable to acarrier frequency of the signal to be transmitted, the primary windingof the transformer being part of the parallel resonance circuit; theparallel resonance circuit comprising a plurality of capacitors that areselectively connected in parallel with the primary winding of thetransformer; the tuning unit comprising a counter that is connected witha clock generator, the counter having outputs that are connected withcontrol inputs of switching transistors for selectively connecting thecapacitors and the windings to the parallel resonance circuit, such thatthe resonant frequency of the parallel resonance circuit changescorresponding to the result of a count of the counter.
 11. The switchingarrangement of claim 10, wherein the parallel resonance circuit furthercomprises tuneable capacitors that are connected in parallel with theprimary winding of the transformer, whereby the resonant frequency ofthe parallel resonance circuit changes corresponding to the result of acontrol voltage applied to the tuneable capacitors in accordance withthe count of the counter.